The blood-brain barrier (BBB) aids in maintaining the protected environment of the CNS; it prevents the free bidirectional passage between blood and CNS interstitial fluid/CSF of many large and small molecular weight, non-lipid soluble substances. Advances in understanding cerebral endothelial function may lead to new therapies for acute brain disorders. Expanding our knowledge of the development of the BBB and the response of the cerebral endothelial cell upon exposure to specific ligands could provide valuable information for circumventing the BBB which would be beneficial in the treatment of certain CNS infections, neoplasm, and enzyme deficiencies. This renewal application focuses on two projects related to the membrane dynamics, organelle interrelationships, and development of the BBB and blood-CSF barrier. Techniques to be employed at light and electron microscopic levels include peroxidase cytochemistry, acid hydrolase cytochemistry, and immunocytochemistry. The first project deals with the potential for receptor mediated and adsorptive endocytosis with subsequent transcytosis (endocytosis followed by transcellular vesicular transport and exocytosis) of circulating proteins, peptides, and positively charge molecules through the cerebral endothelium and choroid epithelium. Molecules that will be administered intravenously or injected into the cerebral ventricles and investigated for transcytosis are wheatgerm agglutinin, transferrin, insulin, albumin, cationized albumin, ferritin, and cationized ferritin. We hypothesize that these macromolecules, excluding native albumin and native ferritin, will undergo transytosis through the cerebral endothelium form blood to brain and through the choroid epithelium form blood to CSF. The second project concerns the angiogenesis and development or absence of a BBB within solid allogafts and cell suspensions of fetal/neonatal CNS, adult non-neural tissue (anterior and posterior lobes of the pituitary gland), PC-12 (pheochromocytoma) cells, and pituitary fenestrated endothelia. The angiogenesis of intercerebral neural and non-neural, grafts/cell suspensions will be investigated under normal conditions and in response to polypeptide mitogens (i.e., epidermal growth factor, endothelial cell growth factor) known to promote amniogenesis; the development or absence of a BBB, as dictated by the tissue/cells introduced to the host CNS, will be analyzed with horseradish peroxidase administered intravenously to the host; the source (host vs. donor) or endothelia supplying intracerebral solid allografts will be assessed immunocytochemically. The long term objectives are to increase our knowledge of the blood-brain and blood-CSF barriers so as to develop new methodologies for delivering blood-borne chemotherapy, peptide pharmaceutical, etc. into the CNS. The proposed investigations will yield additional insight to the cell biology of the cerebral endothelium and application of intracerebral transplants for replacement of lost neurons and/or circumvention of the BBB. These subjects are important in the subspecialties of neurotrauma, neuro-oncology, cerebrovascular disease, CNS deficiencies, and neuronal regeneration.